The present invention generally relates to rotational control apparatus such as clutches and brakes, relates particularly to clutches, relates more particularly to fan clutches, and relates specifically to fan clutches having multiple speed drives and/or which are shock resistant for high torsional and vibration conditions.
Although fan clutches of the type shown in FIGS. 1-3 of U.S. Pat. No. 4,425,993 and in U.S. Pat. Nos. 4,226,095 and 4,877,117 have proven to provide precise power, exceptional economy and dependable, long-lived durability, there exists a need to provide improvements to result in a further advantageous clutch. Specifically, a need exists to provide a multiple speed drive clutch for the fan blades mounted thereon. In particular, in a typical fan clutch application for a truck, while the truck is traveling down the road, the engine is operating at relatively high RPMs and air is rapidly passing by the radiator due to the movement of the truck. Thus, it is not necessary that the fan blades be driven at engine speed under these conditions, and it is advantageous to drive the fan blades at slower speeds or to stop fan rotation for at least noise and/or power consumption reduction reasons. However, when the truck is parked and the engine is idling, maximum cooling is required such that the fan blades are driven at engine speed (or even faster than engine speed). Similarly, cooling requirements for other large engines such as for earth moving equipment or like applications and even for stationary applications vary according to various factors including ambient temperature, air flow, engine speed, and the like.
Further, the axially displaceable components of a fan clutch are subjected to high torsional and vibration conditions due to its interconnection to the crank shaft of the engine which is rotated by the reciprocating action of pistons. High torsional and vibration conditions result in loss of tolerance in the axially displaceable components in preventing relative rotation between the components and in the reduction of the clutch life. Thus, a need exists to provide a clutch which provides a dampening effect within the clutch to increase dependability and long-lived durability and having components which would be damaged by excessive torsional and vibration stress and/or loads being normally replaceable to increase economy.